Objective: The purpose of this study was to evaluate the antimicrobial efficacy of tinidazole. Methods: A total of 51 patients with periodontitis and pericoronitis were selected for this study. Among these patients, 25 of them were treated by local application of metronidazole stilus, and 26 of them were treated with tinidazole stilus. During the same period, patients were sampled, cultured and the bacteria were grown in an anaerobic chamber for 5 ~ 7 days. The MIC50 and MIC90 of tinidazole and metronidazole were determined by using two-fold agar dilution technique against 200 wide-type isolates isolated from patients with periodontitis and pericoronitis.Results: Tindazole had stronger antibacterial activities against Porphyromonas gingivalis, Prevotella, intermedia., Fusobacteruan spp. and Peptostreptococcus spp. The MIC50 and MIC90 were 0.25, 0.25, 0.25, 8and0.5, 0.5, 1, 8 mg/L respectively. The elimination rate was 94.4- 100% . The antimicrobial activity of Tinidazole was significantly stronger than metronidazole ( P
